If you computed 32 bit signed integers F and G from 32 bit signed X using F = X / 2 and G = (X>>1), and you found F!=G, this implies that There is a compiler error X is odd X is negative F - G = 1 G - F = 1
右移和除以2
对于正数的运算得到的结果是一样的，因为最低位被忽略，所以奇数还是偶数无关，结果相等；
对于负数，奇数结果不相等，偶数是结果相等的；而且算出来的结果必然是
F = X / 2 大于 G = (X>>1)，相差也只能是1；
综述，
X is negative 并且
X is odd； F-G=1.
